Powered wheelchair with a detachable power drive assembly

ABSTRACT

A wheelchair (20) including a wheelchair frame (22) and a seat assembly (24) carried by the wheelchair frame (22). A detachable power drive assembly (32) having power driven wheels (40, 40&#39;) is releasably coupled to the wheelchair frame (22) and is mounted for selective removal of the drive assembly (32) as a unit from the wheelchair frame (22). Wheel mounting ports (76, 76&#39;) are also provided in the wheelchair frame (22) for releasably receiving a pair of manually-operable drive wheels (34, 34&#39;). An anti-tip suspension (80) is also provided and includes a suspension arm (84) which is mounted to resist rearward tipping of the wheelchair by a non-linear restoring force. A wheel lock (108) is mounted for movement between a deployed operable position and a stored inoperable position. In the deployed position, the wheel lock (108) extends laterally outwardly of the wheelchair frame (22) for engagement with and braking of manually operable drive wheels (34, 34&#39;).

TECHNICAL FIELD

The present invention relates, generally, to wheelchairs and, moreparticularly, to wheelchairs including power drive assemblies.

BACKGROUND ART

Wheelchairs have been primarily designed to provide transportation forthe physically impaired, often emphasizing user comfort, portability andflexibility. Because of the individual needs and requirements of thewheelchair occupants, however, a variety of styles and shapes have beendeveloped which cater to their specific needs. Moreover, most of thesestyles and shapes include power driven counterparts which, of course,are highly desirable.

Powered wheelchairs generally include an electric powered drive assemblyhaving a drive assembly support structure which forms an integralportion of a wheelchair support frame. Typically, the drive assemblyincludes an electric motor and battery, each of which are generallymounted to the drive assembly support structure. At least two powerdriven wheels, supported by the wheelchair support frame, are rotatablycoupled to the motor and engage the ground to propel the wheelchair.Furthermore, the wheelchair support frame carries a seat supportassembly including a seat and a backrest. The drive assembly is usuallyoperably coupled to a joystick which permits the user to control thedirection of travel of the powered wheelchair from the user operationalposition.

While powered wheelchairs are highly advantageous in many situations,manually propelled or operated wheelchairs also can have manyadvantages. Moreover, if the drive assembly of a powered wheelchairshould malfunction, for whatever cause, the wheelchair occupant may beleft without a functional wheelchair for the duration of the repairperiod. Usually, the motor and/or batteries are individually mounted tothe drive assembly support structure which, in turn, is integrallymounted to the wheelchair support frame. Repair of the damagedcomponents often requires complete removal from the drive assemblysupport structure, and hence, the wheelchair support frame whichinvolves a complex task reserved for the skilled technician. Moreover,removal of the complete drive assembly may require a piecemeal removalof each drive component. That is, the drive assembly cannot be readilyremoved from the wheelchair support frame as an independent unit. Thus,the whole wheelchair apparatus must be brought in for repair. Duringthis repair time, the wheelchair user may be without recourse.

Typical of such prior art powered wheelchair assemblies are thewheelchairs disclosed in U.S. Pat. No. 5,022,476 to Weege; U.S. Pat. No.4,961,473 to Jones; U.S. Pat. No. 4,805,712 to Singleton; and U.S. Pat.No. 4,341,278 to Meyer, each of which describes an electric poweredwheelchair having a drive assembly support structure forming an integralpart of the wheelchair support frame.

Attempts have been made to modularize the drive assembly to aid removalof the components. U.S. Pat. No. 4,967,864 to Boyer et al. discloses apowered wheelchair apparatus having modularized individual componentsformed for easier removal from the drive assembly. While the Boyerwheelchair may facilitate removal of the individual components, thedrive assembly, as a unit, is not removable.

Still other attempts have been made to retrofit independent electricdrive units to manually operable wheelchairs. U.S. Pat. No. 4,767,864and U.S. Pat. No. 4,386,672 to Coker disclose detachable electric driveunits mountable proximate a front portion of the wheelchair. This devicehowever, poses several problems. The forward mounting of the drive unitseverely hampers the user's entry and exit of the wheelchair when thedrive unit is installed, as well as impedes the movement of the useronce situated in the operating position. This problem can be magnifiedfor those users severely impaired. Additionally, the pivotal motion ofthe steering precludes the effective use of footrests for the occupant.

Moreover, powered wheelchairs are often bulkier and substantiallyheavier than their manually operated counterparts. The weight of themotor, in addition to the battery, can be significant. A battery alonemay weigh in excess of 20 lbs. Moreover, two batteries are necessary inmost instances. The wheelchair support frame must also be designed toaccommodate this additional weight which itself adds weight. Thus,wheelchair users often prefer manually operable wheelchairs for homeuse. The additional bulkiness of powered wheelchairs impairsmaneuverability inside close quarters. Further, the power driven wheelstogether with the additional weight can wear or damage the floors andrugs of a home. Accordingly, it is highly advantageous for the user of apowered wheelchair to also own a manually operated wheelchair for homeuse. Unfortunately, this requires the wheelchair user to have twowheelchairs at his or her disposal, which is costly and requires storagespace.

Additionally, if the wheelchair user has only a powered chair, whendrive assembly malfunctions occur, the wheelchair must be pushed aboutmanually. This task is cumbersome and requires assistance because of theadditional weight of the powered chair and the lack of user operabledrive wheels. Thus, dual usage of a powered wheelchair as both a poweredand a manually operated chair has not been practical.

Another problem associated with powered wheelchairs is that they are notas portable as manual wheelchairs. Manually operated wheelchairs aremuch easier to transport in automobiles because they often do notrequire any special vehicle modifications or accommodations. Thecollapsibility of many manually operated wheelchairs makes themparticularly suitable for portability in vehicles. In contrast, mostpowered wheelchairs, because of the integral mounting of the driveassembly onto the support frame, occupy substantially more space and areusually not a collapsible as their manually operated counterparts.Moreover, the additional weight a powered wheelchair carriessubstantially impedes the lifting of the wheelchair into vehicles. Oftenspecial vans or automobiles having modified exteriors and interiors arenecessary to lift and transport powered wheelchairs.

Still other problems associated with powered wheelchairs are that theyhave a tendency to tip backwards upon initial acceleration. The torquegenerated by the motor is often substantial and the unwary user may tipover. In light of this problem, anti-tip caster wheels are oftenprovided rearward of the drive wheels. These caster wheels often aremounted on arms rigidly coupled to the support frame and are angleddownward to a level just above the ground. As the wheelchair begins totip backward, the anti-tip caster wheels engage the ground to preventfurther tipping. Typical of this type of structure is the wheelchair ofU.S. Pat. No. 4,721,321 to Haury et al.

While these anti-tip mechanisms have successfully prevented rearwardtipping of the wheelchair apparatus in most instances, the rigidcoupling of the anti-tip wheel to the support frame provides a fairlyabrupt jolt to the wheelchair occupant as the anti-tip wheel engages theground. In one instance, the occupant's momentum is pivoting rearwardabout the drive wheel axis; in another instance the occupant's momentumis shifted forward as the anti-tip wheel engages the ground. Thismomentum shift may jolt the occupant which can be physically tolling,particularly on those severely impaired.

Accordingly, it is an object of the present invention to provide awheelchair apparatus which is operable as both a powered and a manuallymovable wheelchair.

Another object of the present invention is to provide a wheelchairapparatus with a removably mounted drive assembly.

It is another object of the present invention to provide a poweredwheelchair apparatus which is more portable.

Still another object of the present invention is to provide a poweredwheelchair apparatus which lowers the composite center of gravity.

Yet another object of the present invention is to provide aprogressively rated anti-tipping suspension to a wheelchair apparatus.

It is a further object of the present invention to provide a wheelchairapparatus which is durable, compact, easy to maintain, has a minimumnumber of components, is easy to use by unskilled personnel, and iseconomical to manufacture.

The apparatus and method of the present invention has other objects andfeatures of advantage which will be more readily apparent from thefollowing description of the best mode of carrying out and invention andthe appended claims, when taken in conjunction with the accompanyingdrawing.

DISCLOSURE OF INVENTION

The present invention includes a wheelchair comprising a wheelchairframe having a fore and an aft portion, and a seat assembly carried bythe wheelchair frame. The wheel chair further includes power driveassembly with a drive assembly frame and a motor mounted to the driveassembly frame. Power drive wheels also are mounted to the driveassembly frame and are operably coupled to the motor. A drive assemblymounting mechanism releasably couples the drive assembly frame to thewheelchair frame proximate the aft portion of the wheelchair frame fordriving of the wheelchair as a powered wheelchair and for selectiveremoval of the power drive assembly as a unit from the wheelchair frame.Wheel mounted assemblies are also provided on the wheelchair frame toreleasably receive a pair of manually-operable drive wheels. These drivewheels permit manual operation of the wheelchair apparatus when thepower drive assembly is removed from the wheelchair frame.

In another aspect of the present invention an anti-tip suspension forthe wheelchair is provided comprising a suspension arm assembly having amounting mechanism for pivotally mounting the arm assembly to thewheelchair frame. The arm assembly includes a first arm portion whichextends away from the mounting mechanism. A ground engaging device isprovided on the first arm portion at a spaced distance from the mountingmechanism. Furthermore, the suspension arm assembly includes a pivotalmotion resisting mechanism which resists pivoting of the first armportion about the mounting mechanism when the wheelchair is tipped by anamount sufficient to cause the ground engaging device to contact theground.

In yet another aspect of the present invention, a wheel lock assemblyfor a wheelchair is provided mounted to the wheelchair frame and formedto engage at least one of the manually-operable drive wheels to effectlocking of the wheels thereof. The wheel lock assembly is mounted formovement between a deployed operable position and a stored inoperableposition. In the deployed operable position, the wheel lock assemblyextends laterally outwardly of the wheelchair frame by an amountenabling frictional engagement by the wheel lock assembly with one ofthe manually-operable drive wheels to effect braking thereof. In thestored position, the parking brake assembly is located laterallyinwardly of the wheelchair frame.

These and other features and advantages of the present invention willbecome more apparent from the following description of exemplaryembodiment thereof, as illustrated in the accompanying drawing.

BRIEF DESCRIPTION 0[THE DRAWING

FIG. 1 is a top perspective view of a wheelchair apparatus constructedin accordance with the present invention and including a detachablepower assembly.

FIG. 2 is a schematic, top perspective view of the wheelchair apparatusof FIG. 1 with the power assembly removed and manually-operable wheelsmounted thereto.

FIG. 3 is an enlarged, top perspective view of the detachable driveassembly constructed in accordance with the present invention.

FIG. 4 is a top plan view of the detachable drive assembly of FIG. 3.

FIG. 5 is a rear elevation view of the detachable power assembly of FIG.3 and illustrating the mounting spacers.

FIG. 6 is a fragmentary, enlarged, schematic side elevation view of thedetachable drive assembly mounting mechanism.

FIG. 7 is an enlarged, side elevation view of the anti-tip suspensiondesigned in accordance with the present invention.

FIG. 8 is an enlarged, top perspective view of the manual wheel lockassembly constructed in accordance with the present invention andillustrating a "deployed" position.

FIG. 9 is a top perspective view of the manual wheel lock assembly ofFIG. 8 and illustrating a "stored" position.

FIG. 10 is a side elevation view, partially broken away, of the manualwheel lock assembly of FIG. 8 and showing the spring assembly.

BEST MODE OF CARRYING OUT THE INVENTION

The wheelchair apparatus of the present invention includes a detachabledrive assembly removably mounted to a wheelchair frame. The driveassembly is detachable as an independent unit from the wheelchair frameso that the wheelchair apparatus may be manually operable. The followingdescription is presented to enable a person skilled in the art to makeand use the invention, and is provided in the context of a particularapplication and its requirements. Various modifications to the preferredembodiment will be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to other embodimentsand applications without departing from the spirit and scope of theinvention. Thus, the present invention is not intended to be limited tothe embodiment shown, but is to be accorded with the widest scopeconsistent with the principles and features disclosed herein.

It will be noted here that for a better understanding, like componentsare designated by like reference numerals throughout the variousfigures. Attention is now directed to FIG. 1, where the subjectwheelchair apparatus, generally designated 20, is illustrated. Assembly20, briefly, comprises a wheelchair frame means, generally designated22, which carries a seat assembly 24 having a seat member 26 and abackrest member 28. A pair of front caster wheels 30 are pivotallymounted proximate a fore portion of wheelchair frame means 22 whichprovide support and aid steering. Detachably mounted proximate an aftportion of frame means 22 is an independent power drive assembly unit,generally designated 32, which provides powered mobility to wheelchairapparatus 20.

As will be described in greater detail below, drive assembly 32 isremovably mounted proximate the aft portion of wheelchair frame means 22and operates as a rear wheel drive mechanism for wheelchair apparatus20. Drive assembly 32 is fully independent of frame means 22 and isformed for selective removal as a unit. When drive assembly 32 isdetached from wheelchair frame means 22, manually-operable wheels,generally designated 34 and 34', may be removably mounted directly toframe means 22, as illustrated in FIG. 2. Therefore, wheelchairapparatus is fully operable as either a powered wheelchair (FIG. 1), ora manually-operable wheelchair (FIG. 2) wherein wheelchair frame means22 is free of any power drive assembly components.

The detachable power assembly configuration of the present invention ishighly beneficial for numerous reasons. For example, this constructionaffords enhanced portability of the wheelchair apparatus, facilitatesrepair of the drive assembly, and eliminates the need to have more thanone wheelchair. Transportation of wheelchair apparatus 20 is facilitatedby the removal of power drive assembly 32 as an independent unit. Thecurrent commercially available powered wheelchairs, where the driveassemblies are not removable as a unit, are often too heavy to lift as awhole or would require substantial disassembly to remove the integrallymounted drive unit. In contrast, removal of power drive assembly 32 inaccordance with the present invention, a fairly simple procedure. Onceremoved, the weight of wheelchair apparatus 20 is substantially reducedso that it may be more easily lifted or moved. Similarly, drive assembly32, once removed from the main wheelchair frame, is lighter and lessbulky. This detachable construction, therefore, greatly eases wheelchairportability.

Furthermore, should power drive assembly 32 malfunction, it can easilybe detached from wheelchair frame means 22 and independently brought toa shop for repair as a unit, rather than requiring the whole wheelchairapparatus 20 to be brought into the shop. Moreover, power driveassemblies 32 can be interchangeable so that should the individual'spower drive assembly 32 need repair, a replacement drive assembly 32 maybe used in the repair interim. This substantially eliminates "down time"of the powered wheelchair apparatus 20 during repair time.

Because wheelchair apparatus 20 is fully operable as a manual wheelchair(FIG. 2), it may not be a necessary to own both a manual chair inaddition a powered chair. For example, for home use or in closeconfines, power drive assembly 32 may simply be detached from wheelchairframe means 22 and replaced with manually operable wheels 34 and 34'.Accordingly, manually-operable wheelchair apparatus 20 will not undulywear or harm the rung and floors the way a powered wheelchair may.

Power drive assembly 32 can be seen in FIG. 3-5, include a drive framemeans 36 suitably formed to support motor means, generally designated38. Motor means 38 is drivably coupled to a pair of powered wheels 40and 40' which are standard wheels employed by various poweredwheelchairs. In the preferred embodiment, motor means 38 is provided bytwo motors 39 and 39' (FIGS. 4 and 5) are employed, each of which drivesone powered wheel 40 and 40', and each of which are centrally mounted todrive frame means 36. This configuration is especially beneficial infacilitating short radius turns. Each motor 39 and 39' may drive thecorresponding powered wheel 40 and 40' in opposite rotational directionswhich will turn wheelchair apparatus 20 about a much smaller radius.

Motors 39 and 39' are preferably common electric motors generally knownin the field. It will be appreciated, however, that a combustion motoror other equivalent device employed to power wheels 40 and 40' could beused without departing from the true spirit and nature of the presentinvention.

Power drive assembly 32 further includes an electronic controller unit42 which is operably coupled to a joystick device 44 (FIGS. 1 and 2)mounted proximate seat assembly 24. Accordingly, the user may easilycontrol the operation and direction of wheelchair apparatus 20 from aseated position.

Because two independent motors 39 and 39' are employed by power driveassembly 32, it is also preferable to include two independent batteries46 and 46' (i.e., one for each motor). As shown in FIGS. 3 and 4,batteries 46 and 46' (preferably encased in battery covers) are mountedto drive frame means 36 on opposite sides of centrally mounted motors 39and 39'. This mounting symmetry balances most of the weight of driveassembly 32 about a horizontal axis extending through the drive axles 41and 41'. As will be discussed in more detail below, drive assembly 32includes adjustments which permit the positioning of drive assembly 32relative to the wheelchair frame in a manner allowing the overall centerof gravity of the chair to be adjusted. This symmetry of the driveassembly weight also reduces the moment of inertia about a verticalaxis, which permits wheelchair apparatus 20 to turn easily at a smallturn radii and enables a more controlled turn acceleration, as comparedto current commercially available wheelchair assemblies. Thisconsiderably facilitates user maneuverability, particularly in smallconfines.

Furthermore, FIG. 1 illustrates that power drive assembly 32 is compactand is situated fairly low to the ground relative to wheelchair framemeans 22. Because the weight of drive assembly 32 represents asubstantial percentage of the overall weight of wheelchair apparatus 20,the cumulative wheelchair apparatus center of gravity (CG) will also belowered. This configuration (i.e., lowered CG) minimizes lateral tippingof wheelchair apparatus 20 during the above-mentioned small radius turnsor the like.

Wheelchair frame means 22 includes two substantially parallel,trapezoidal side frame members 48 and 48' (FIGS. 1 and 2) rigidlycoupled together by a crossbar members 50. Trapezoidal side framemembers 48 and 48' and cross-members 50 are preferably hollowrectangular tube structures of sufficient rigidity and thickness tosupport and carry seat assembly 24 and its passenger. Trapezoidal sideframe members 48 and 48' are preferably formed to be positioned adjacentto and on opposite sides of power drive assembly 32 so as to straddleit, as shown in FIG. 1. This eases mounting and positioning of powerdrive assembly 32 relative to wheelchair frame means 22.

Power drive assembly 32 is detachably mounted to wheelchair frame means22 through a mounting assembly, generally designated 52. As best viewedin FIGS. 1 and 6, mounting assembly 52 includes a first mounting element54 secured by fasteners 55 to an inner side of side frame member 48 anda second mounting element 56 carried by drive frame means 36. Mountingassembly 52' similarly includes a first mounting element 54' and asecond mounting element 56'. Both first mounting elements 54 and 54',and corresponding second mounting elements 56 and 56' are convergentlytapered in a downward direction and formed for mating nested engagementwith one another. Thus, each first mounting element 54 and 54' includesdownwardly facing wedge-shaped surface 58 which promotes mountingstability with mating surface 60 of second mounting element 56 and 56'.It will be appreciated that both first mounting element 54 and 54' andsecond mounting element 56 and 56' could be convergently tapered in aupward direction, with the female receiving element mounted to framemembers 48 and 48' and the male elements mounted to frame means 36.Moreover, first mounting element 54 and 54' and second mounting element56 and 56' could include rounded male-female mating members orpin-and-socket mating members without departing from the true spirit andnature of the present invention.

A threaded fastener 62, as shown in FIG. 6, permits releasable mountingof first mounting element 54 to corresponding second mounting element56. Fastener 62 preferably includes a bolt portion 64 extending throughfirst mounting element 54. Bolt portion 64 is received in acorresponding threaded opening 66 provided in an upward facing surface68 of second mounting element 56. Virtually any quick release fastenermay be employed, however. When bolt portion 64 is threadably fastened inopening 66, the downwardly facing wedge-shaped surface 58 of firstmounting element 54 matingly engages the upwardly facing mating surface60 of second mounting element 56. Accordingly, mounting assembly 52provides an accurate, rigid, yet quick release mounting method of powerdrive assembly 32 to wheelchair frame means 22.

FIG. 6 further illustrates that each second mounting element 56 and 56'may be situated at a plurality of positions along the sides of driveframe means 36. A plurality of alignment bores 70 extend through a sideportion of each second mounting element 56 and 56'. Alignment ofselective alignment bores 70 with corresponding mounting holes (notshown) extending through drive frame means 36 permit second mountingelement 56 and 56' to moved between a fore and an aft portion relativeto drive frame means 36. Alignment fasteners 72 are used to releasablymount second mounting elements 56 and 56' to drive frame means 36.Adjusting second mounting elements 56 and 56' between the fore and theaft portion of drive frame means 36 allows favorable positioning ofpower drive assembly 32 relative to the vertical axis extending throughthe combined wheelchair center of gravity. In turn, the moment ofinertia about such vertical axis can be minimized to facilitate turningacceleration, as mentioned above.

Turning now to FIGS. 4 and 5, spacers 74 and 74' may be provided, ofvarying thickness, between drive frame means 36 and second mountingelements 56 and 56'. Spacers 74 and 74' position second mountingelements laterally outward from drive frame means 36. This permitsprecise alignment of second mounting element 56 and 56' with thecorresponding first mounting element 54 and 54' for wheelchair framemeans 22 having different width dimensions, i.e., cross-members 50 ofdiffering length. Thus, the detachable power drive assembly of thepresent invention can be mounted to wheelchairs of customized widthsimply by changing spacers 74 and 74'.

In accordance with the present invention, power drive assembly 32 may bedetached from wheelchair frame means 22, as a unit, and wheelchairapparatus 20 may be operated as a manually powered wheelchair. As bestshown in FIG. 2, a pair of preferably 2441 diameter manually-operablewheels 34 and 34' are releasably mounted to wheelchair frame means 22.Manual wheel mounting passageways 76 and 76' are provided proximate theaft portions of each trapezoidal side frame member 48 and 48'. Mountingpassageways 76 and 76' are dimensioned to releasably receive the axleportions 75' of manually-operable wheels 34 and 34'. In the preferredform, wheels 34 and 34' include quick release hubs 78 and 78' commonlyknown in the field which provide quick release of wheels 34 and 34' frommounting passageways 76 and 76'.

Mounting passageways 76 and 76' are positioned vertically on trapezoidalframe members 48 and 48' at a level which preferably positions seatassembly 24 at a height substantially similar to the seating height whendrive assembly 32 is mounted to wheelchair frame means 22. It is notedthat the vertical positioning of mounting passageways 76 and 76' couldbe adjustable so as to accommodate different diameter manually operablewheels, if desired. Similarly, the fore and aft positioning of mountingpassageways 76 and 76' along trapezoidal frame members 48 and 48' isselected to position the manually-operable wheels 34 and 34' atsubstantially the same location as powered-wheels 40 and 40' of driveassembly 32. This assures that the mobility characteristics between thepowered wheelchair apparatus and the manually operable wheelchairapparatus are not radically different. It also will be understood that aplurality of fore and aft locations for passageways 76 and 76' could beprovided.

In another aspect of the present invention, it is recognized thatangular acceleration of power driven wheels 40 and 40' can causewheelchair apparatus 20 to tip rearward. Thus, an anti-tip suspension,generally designated 80, is provided which non-linearly resists rearwardtipping of wheelchair apparatus 20 during abrupt accelerations. As bestviewed in FIGS. 3 and 7, anti-tip suspension, generally designated 80,includes a pair of suspension arm assemblies 84 and 84' pivotallymounted to opposite sides of drive frame means 36. Although preferablytwo independent suspension arm assemblies 84 and 84' are provided, itwill be understood that a single suspension arm assembly 84 mayadequately provide the desired variable rate resistance necessary toprovide a suspension function and an anti-tipping function. Moreover, itis noted that anti-tip suspension 80 can be pivotally mounted towheelchair frame means 22 rather than drive frame means 36 withoutdeparting from the true spirit and nature of the present invention. Forbrevity, only one suspension arm assembly 84 will be described indetail.

Suspension arm assembly 84 is formed to provide a variable rateresistance to displacement which progressively increases as suspension80 increasingly engages the ground 82. When suspension arm assembly 84is vertically compressed, as shown in phantom lines in FIG. 7, theresistance rate of suspension 80 increases non-linearly furtherresisting rearward tipping. This configuration has been found to providea smooth transitional force opposing tipping. The nonlinear resistanceeliminates the abrupt stops or severe jolts commonplace in the prior artanti-tipping devices provided. Furthermore, the force returningwheelchair 20 to its normal stable position, with front caster wheels 30on ground 82, also decreases nonlinearly so as not to throw or launchthe occupant forward as front caster wheels 30 once again engage ground82. Accordingly, the present invention effectively resists rearwardtipping and gently returns wheelchair 20 to its normal operatingposition. By comparison, the relatively rigid cantilever-type anti-tipdesigns of the prior art are not specifically designed for progressiveresistance and generally are formed merely as anti-tipping stops.Engagement, upon rearward tipping, with these devices is often abruptand jolting to the user.

Moreover, and very importantly, the variable resistance feature allowsarm 84 to support wheel 94 very close to support surface 82, as bestseen in FIG. 7. This positioning, less than one inch above supportsurface 82 could not be tolerated if arm 84 were rigidly mounted to thewheelchair. The resilient, nonlinear support of arm 84, however, allowsit to have a ground engaging means, such as a wheel 94, positioned closeto the ground so as to almost immediately start to resist tipping withan initially low force that increases with increased displacement. Thissmooths the resistance to tipping so as to reduce jolting and jarring ofthe rider. Moreover, small bumps and undulations in support surface 82can be easily accommodated by displacement of wheel 94 and arm 82upwardly against a resistance force that is relatively low duringinitial arm displacement and increases smoothly if large displacementsoccur.

As best shown in FIGS. 1 and 3, suspension arm assemblies 84 and 84' arepreferably positioned proximate the aft portion of drive frame means 36.Suspension arm assembly 84 includes a first or pivotal arm portion 86extending downward and away from, and mounted for pivotal movementabout, a first stationary mount or pivot pin 88. A second or sliding armportion 90 extends away from first stationary mount 88 in the aftdirection, and includes a flexible apex or knee portion 92 extendingfrom the upper end of pivotal am portion 86 proximate first stationarymount 88. Accordingly, sliding arm portion 90 and pivotal arm portion 86diverge from knee portion 92 forming a V-shaped suspension arm assembly84 with each arm portion defining one side of the V. A ground engagingwheel 94 preferably is rotatably mounted to the lower end of pivotal armportion 86.

Suspension 80 is movably mounted about two stationary mounts which aresecured to drive frame means 36. The first stationary mount 88, alreadydescribed above, provides pivotal displacement of pivotal arm portion 86about first stationary mount 88. A second stationary mount 96 ispositioned proximate an upper end of sliding arm portion 90 oppositeknee portion 92. Second stationary mount 96 is formed and dimensioned toslidingly engage a slot 100 provided in the upper end of sliding armportion 90. Slot 100 extends longitudinally along sliding portion 86 andis formed to prevent rotation of sliding arm portion 90 about firststationary mount 88. However, slot 100 permits sliding translationalmovement of sliding arm portion 90 relative to second stationary mount96 for the reasons to be described henceforth.

In accordance with the present invention, suspension arm assembly 84non-linearly and progressively increases resistance against rearwardtipping as the end portion of pivotal arm portion 86 verticallydisplaces relative to sliding arm portion 90. As shown in phantom linesin FIG. 7, V-shaped suspension arm assembly 84 is resiliently flexibleabout knee portion 92. This resilient flexibility permits substantialvertical displacement of the lower end portion of pivotal arm portion 86when ground engaging caster wheel 94 engages ground 82. Knee portion 92includes a flexibility opening 102 extending substantially horizontallythrough knee portion 92. Opening 102 provides greater flexibility andmore displacement of pivotal arm portion 86 about first stationary mount88.

An upward facing cam surface 104 is provided on pivotal arm portion 86which is positioned to engage an opposing contact surface 106 on slidingarm portion 90. As shown in the phantom lines of FIG. 7, duringsubstantial upward displacement of pivotal arm portion 86 about firststationary point mount or pin 88 (e.g., when wheelchair apparatus 20 istipped substantially rearward), cam surface 104 is drawn into rockablecontact with opposing contact surface 106. The initial contact betweencam surface 104 and opposing contact surface 106 occurs proximate pivotpin 88 so that the resistance to flexing of knee portion 92 isrelatively low. However, as cam surface 104 increasingly engagesopposing contact surface 106, the curvature of cam surface 106 causesthe contact to occur at a greater radial distance from pivot pin 88which, further, causes sliding arm portion 90 to slightly bow. Thisincreases the resistance to upward pivoting in a non-linear manner.Furthermore, pivoting of suspension arm 84 about first stationary mount88 also causes sliding translational movement of sliding arm portion 90,via slot 100, with respect to second stationary mount 96. Thus, theabove-mentioned combination of conditions culminate to provide anon-linearly increasing resistance force against rearward tipping.

Because it is desirable for sliding arm portion 90 to slightly bow orflex as cam surface 104 increasingly engages contact surface 106,sliding arm portion 90 is preferably composed of a material slightlymore resilient or flexible than pivotal arm portion 86. Therefore,although suspension arm assembly 84 is preferably a unitary structure,sliding arm portion 90, pivotal arm portion 86 and knee portion 92 maybe composed a combination of different resilient semi-flexiblematerials. For example, composite plastics or the like are particularlysuitable. In this manner, the non-linear resistance can be programmedfor a particular use. Moreover, the cross-sectional configurations anddimensions of sliding arm portion 90, pivotal arm portion 86 and kneeportion 92 may be varied to program the desired non-linear resistanceproperties.

In still another aspect of the present invention, a wheel lock assembly,generally designated 108, is provided to effect locking ofmanually-operable wheels 34 and 34' during manual operation ofwheelchair apparatus 20 (i.e., when power drive assembly 32 isdetached). In accordance with the present invention, wheel lock assembly108 is mounted for movement between a "deployed" operable position (FIG.8) and a "stored" inoperable position (FIG. 9). It will be understoodthat the "deployed" position represents the orientation of wheel lockassembly 108 in which it may be extended into frictional engagement withthe corresponding manually-operable wheel 34 to effect locking thereof.In this orientation, wheel lock assembly 108 may be moved between one oftwo positions. The first "deployed" position corresponds to anon-locking position (shown in solid lines in FIG. 8) which is free offrictional engagement with manually-operable wheels 34 and 34'. Thesecond "deployed" position (shown in phantom lines) corresponds to alocking position in which wheel lock assembly 108 is extended to effectlocking of manually-operable wheels 34 and 34'. Thus, the "deployed"position is typical of the standard, fixed orientation of the wheel lockassemblies employed on most prior art wheelchair assemblies.

In contrast, the "stored" position (FIG. 9) of the present inventioncorresponds to an orientation which places wheel lock assembly 108 outof reach and stowed for non-use. This stowed position is particularlyuseful when power drive assembly 32 is attached to wheelchair framemeans 22 and manually-operable wheels 34 and 34' are dismountedtherefrom. Because wheel lock assembly 108 is inoperable to effectlocking when wheelchair apparatus 20 is arranged to be power driven,manual wheel lock assembly 108 is a potential nuisance in someinstances. Accordingly, it is preferable to reposition wheel lockassembly 108 out of operable use.

Wheel lock assembly 108 includes a first mounting member 110 carrying awheel engaging means 112 mounted on one end thereof which is suitablyformed for frictional engagement with manually-operable wheel 34. Wheelengaging means 112 is similar to most common manual wheel locks employedin the industry. A second mounting member 114 is rigidly fixed towheelchair side frame means 48 proximate an upper cross-frame member 50.(Note that the wheelchair is reversed in position in FIGS. 8-10 from theposition of FIGS. 1 and 2.) Mounting member 114 is formed anddimensioned for sliding rotatable engagement with first mounting member110. This arrangement permits first mounting member 10 to be rotatablypositioned in either the "deployed" position (FIG. 8) and the "stored"position (FIG. 9).

First mounting member 110 includes a post member 116 formed to extendlaterally along wheelchair frame means 22. Second mounting member 114 ispreferably a sleeve-like member providing a post receiving opening 118which is formed and dimensioned to slidably receive an end of postmember 116. Accordingly, post member 116 is telescopically mounted forpivotal movement relative to opening 118 between the "stored" inoperableposition and the "deployed" operable position. It will be appreciatedthat the post member/receiving opening arrangement between firstmounting member 110 and second mounting member 114, respectively, may bereversed without departing from the true spirit and nature of thepresent invention.

An alignment slot 120 is provided proximate the distal end of postmember 116, as best shown in FIGS. 9 and 10. Alignment slot 120 isformed and dimensioned to slidably receive an alignment bar 122positioned inside post receiving opening 118. The proper positioning andinterengagment between alignment slot 120 and alignment bar 122 orientwheel lock assembly 108 in either the "deployed" position or the"stored" position. As post member 116 is telescopically received inopening 118, wheel lock assembly 108 is approximately positioned ineither the "deployed" position or the "stored" position whereinalignment slot 120 will matingly engage and receive alignment bar 122provided in bore 118 and extending transversely thereacross. It is notedthat the "stored" position is preferably rotated approximately 180Degrees from the "deployed" position. Upon interengagement therebetween,wheel lock assembly 108 will be more precisely aligned in one of theabove-mentioned positions.

As shown in FIGS. 9 and 10, a quick-release locking pin 124 releasablylocks post member 116 relative to receiving opening 118 in either the"deployed" position or the "stored" position. Hence, alignment bar 122will not inadvertently disengage from alignment slot 120 so that firstmounting member 110 is free to pivot about second mounting member 114.In the preferred form, complimentary locking bores 126 are provided inand extend through both post member 116 and sleeve-shaped secondmounting member 114. Locking bores 126 are formed and dimensioned toreceive locking pin 124, and are positioned to cooperate with thealignment slot/bar to releasably lock wheel lock device 108 in eitherthe "stored" or the "deployed" position. After locking pin 124 has beeninserted through locking bores 126, the positioning of post member 116relative to receiving opening 118 will be releasably preserved.

In an alternative embodiment of wheel lock assembly 108, a retainingspring member 128 is coupled between telescopically mounted post member116 and post receiving opening 118, as viewed in FIG. 10. Retainingspring member 128 resiliently retains post member 116 telescopicallymounted relative to opening 118 to facilitate interengagement betweenalignment slot 120 and alignment bar 122 before locking pin 124 isinserted into locking bores 126. Retaining spring member 128 ispreferably a coil-type tension spring having one end coupled toalignment bar 122 and the opposing end mounted inside post member 116.Spring member 128 is formed to permit pivotal movement of post member116 relative to post receiving opening 118.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed embodiment but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

Therefore, persons of ordinary skill in this field are to understandthat all such equivalent structures are to be included within the scopeof the following claims.

What is claimed is:
 1. A wheelchair comprising:a wheelchair frame havinga fore portion and an aft portion; a seat assembly carried by saidwheelchair frame; a power drive assembly including a drive assemblyframe, a motor mounted to said drive assembly frame, at least one powerdrive wheel mounted to said drive assembly frame and operably coupled tosaid motor; said power drive assembly being removably coupled to saidaft portion of said wheelchair frame by a mounting structure including afirst mounted element carried by said wheelchair frame, a secondmounting element carried by said drive assembly frame, and a fastenerreleasably coupling said first mounting element to said second mountingelement, said second mounting element including a positioning structurefor coupling said second mounting element to said drive assembly frameat a plurality of positions changing the location of a center of gravityof said wheelchair; and a wheel mounting structure provided on said aftportion of said wheelchair frame and formed to releasably receive a pairof manually operable drive wheels for mounting to said wheelchair framewhen said power drive assembly is removed from said wheelchair frame. 2.The wheelchair as defined in claim 1 wherein,said positioning structureis formed for coupling said second mounting element at one of aplurality of positions along a length of said drive assembly frame. 3.The wheelchair as defined in claim 2 wherein,said positioning structureincludes a plurality of apertures extending through said second mountingelement,
 4. The wheelchair as defined in claim 1 wherein said wheelchairfurther includes:an anti-tip suspension assembly mounted to said driveassembly frame and extending rearwardly and downwardly therefrom to aposition rearward of said power drive wheel and above the ground toprevent rearward tipping of said wheelchair.
 5. A wheelchaircomprising:wheelchair frame having a fore portion and an aft portion; aseat assembly carried by said wheelchair frame; a power drive assemblyincluding a drive assembly frame, a motor mounted to said drive assemblyframe, and power drive wheels mounted to said drive assembly frame andoperably coupled to said motor; a drive assembly mounting structurereleasably coupling said drive assembly frame to said wheelchair frameproximate said aft portion; a wheel mounting structure provided on saidwheelchair frame and releasably receive a pair of manually-operabledrive wheels for mounting to said wheelchair frame means when said powerdrive assembly is removed from said wheelchair frame; and an anti-tipsuspension assembly mounted to one of said aft portion of saidwheelchair frame and said drive assembly frame for preventing rearwardtipping on said wheelchair, said anti-tip suspension assembly includinga suspension are assembly, and a mounting structure pivotally mountingsaid arm assembly to said one of said wheelchair frame and said driveassembly frame, said arm assembly having a first arm portion extendingaway from said mounting structure, and ground engaging element providedon said first arm portion at a spaced distance from said mountingstructure and in a normally elevated position above the ground, and saidarm assembly further including pivotal motion resisting structureresisting pivoting of said first arm portion about said mountingstructure when said wheelchair is tipped by an amount sufficient tocause said ground engaging element to move from said elevated positioninto contact with the ground.
 6. The wheelchair as defined in claim 5wherein,said pivotal motion resisting structure resists pivoting of saidfirst arm portion about said mounting structure with a nonlinearresistance force.
 7. The wheelchair as defined in claim 5 wherein,saidpivotal motion resisting structure is provided by a second arm portionon said arm assembly coupled to said first arm portion.
 8. Thewheelchair as defined in claim 7 wherein,said second arm portion andsaid first arm portion extend away from said mounting structure and areformed to cooperatively engage each other to produce said nonlinearresistance force.
 9. The wheelchair as defined in claim 8 wherein,saidsecond arm portion is secured proximate a distal end thereof to saiddrive assembly frame and is further formed for resilient flexing thereofintermediate said distal end and said mounting structure to resilientlyresist rotation of said first arm portion.
 10. The wheelchair as definedin claim 9 wherein,said second arm portion is secured proximate saiddistal end for sliding translational movement.
 11. The wheelchair asdefined in claim 9 wherein,said first arm portion and said second armportion are formed for cooperative engagement after a predeterminedrotation of said first arm portion to progressively increase theresistance to further rotation of said first arm portion.
 12. Awheelchair comprising:wheelchair frame having a fore portion and anafter portion; a seat assembly carried by said wheelchair frame; a powerdrive assembly including a drive assembly frame, a motor mounted to saiddrive assembly frame, and at least one power drive wheel mounted to saiddrive assembly frame and operably coupled to said motor; a driveassembly mounting structure releasably coupling said drive assemblyframe to said wheelchair frame proximate said aft portion for driving ofsaid wheelchair as a powered wheelchair, said drive assembly mountingstructure including a downwardly convergently tapered first mountingelement carried by said wheelchair frame, and a downwardly convergentlytapered second mounting element carried by said drive assembly frame,and fastener means releasably coupling said first mounting element tosaid second mounting element in mating nested engagement; and a wheelmounting structure provided on said wheelchair frame and formed toreleasably receive a pair of manually-operable drive wheels for mountingto said wheelchair frame when said power drive assembly is removed fromsaid wheelchair frame for operation of said wheelchair as amanually-powered wheelchair.